It's possible to override the grid gallery in front-end of the view "creat article".
Please follow this path:
You need to copy this file in this path: \components\com_tz_portfolio_plus\addons\mediatype\grid_gallery\tmpl\default.php
and paste it into the: /templates/your_template/html/ [plg_mediatype_grid_gallery/file.php]
Then start to override, but remeber you need to modify it very carefully.